Preparation of 4-fluoro-3-phenoxy-benzal-dehyde acetals and intermediates therefor

ABSTRACT

The new compound ##STR1## is prepared and converted to the new acetal ##STR2## which is reacted with an alkali phenolate or alkaline earth metal phenolate in the presence of copper or a copper compound as a catalyst and in the presence of a diluent at a temperature between about 100° and 200° C. to produce the new acetal ##STR3## which can be hydrolyzed to the corresponding aldehyde which is a known intermediate for pyrethroid-like insecticides.

This is a continuation of application Ser. No. 174,762, filed Aug. 4,1980, and now abandoned.

The invention relates to certain new 4-fluoro-3-phenoxy-benzaldehydeacetals, to an unobvious process for their preparation and to3-bromo-4-fluoro-benzaldehyde, which is new, and acetals thereof and topreparative processes for these compounds.

It is known that 4-fluoro-3-phenoxy-benzaldehyde, an intermediateproduct for pesticidally active pyrethroids, is obtained when4-fluoro-3-phenoxy-benzyl bromide is reacted with hexamethylenetetramineand the product of this reaction is heated with acids (see DE-OS (GermanPublished Specification) 2,709,264). However, the yields in thissynthesis method and also in the preparation of the starting compoundfrom 4-fluoro-3-phenoxy-toluene and N-bromo-succinimide areunsatisfactory.

The present invention now provides:

(1), as new compounds, the 4-fluoro-3-phenoxy-benzaldehyde acetals ofthe general formula ##STR4## in which the two radicals R individuallyrepresent alkyl or together represent alkanediyl (alkylene);

(2) a process for the preparation of a compound of the formula (I),characterized in that a 3-bromo-4-fluorobenzaldehyde acetal of thegeneral formula ##STR5## in which R has the meaning indicated above

is reacted with an alkali metal phenolate or alkaline earth metalphenolate in the presence of copper or a copper compound as a catalystand in the presence of a diluent, and if appropriate in the presence ofan auxiliary selected from alkali metal halides and carbonates andalkaline earth metal halides and carbonates, and if appropriate in thepresence of a basic dehydrating agent, at a temperature between about100° and 200° C.;

(3) the use of the compounds of the formula (I) as intermediate productsfor the preparation of 4-fluoro-3-phenoxy-benzaldehyde by reaction withacids by known methods for splitting acetals;

(4), as new compounds, 3-bromo-4-fluoro-benzaldehyde acetals of thegeneral formula ##STR6## in which the two radicals R individuallyrepresent alkyl or together represent alkanediyl (alkylene);

(5) a process for the preparation of a compound of the formula (II),characterized in that 3-bromo-4-fluoro-benzaldehyde, of the formula##STR7## is reacted with an alkanol or alkanediol, if appropriate in thepresence of a catalyst and/or a water-binding agent, and if appropriateusing a diluent, at a temperature between about 0° and 150° C.;

(6), as a new compound, 3-bromo-4-fluoro-benzaldehyde, of the formula##STR8## and (7) a process for the preparation of3-bromo-4-fluoro-benzaldehyde, characterized in that a3-bromo-4-fluoro-benzene of the general formula ##STR9## in which R¹represents CH₃ or --CH₂ --OH, is converted into the aldehyde in thecustomary manner.

Surprisingly, 4-fluoro-3-phenoxy-benzaldehyde can be prepared in asimpler manner and in a better yield via the abovementioned newintermediate products than by the abovementioned known process.

Formula (I) provides a definition of the new4-fluoro-3-phenoxy-benzaldehyde acetals. Preferably, in this formula,

the radicals R individually represent C₁ -C₄ -alkyl or togetherrepresent C₂ -C₅ -alkanediyl, especially --CH₂ --CH₂ --.

If 3-bromo-4-fluoro-benzaldehyde propyleneacetal and potassium phenolateare used as starting compounds, the process described under (2) for thepreparation of the new 4-fluoro-3-phenoxy-benzaldehyde acetals ("process(2)") can be outlined by the following equation: ##STR10##

Alkali metal phenolates and alkaline earth metal phenolates which can beused as starting substances in process (2) are, for example, sodiumphenolate, potassium phenolate and magnesium phenolate. Sodium phenolateis the preferred starting compound.

Copper or copper compounds are used as the catalysts. Examples of thesecatalyst which may be mentioned are copper, copper-(I) oxide,copper-(II) oxide, copper-(I) chloride and copper-(I)bromide.

Aprotic polar solvents are preferably used as the diluents in process(2). Examples of these solvents are dimethylformamide,dimethylacetamide, N-methylpyrrolidone, dimethylsulphoxide,tetramethylene sulphone, hexamethylphosphoric acid triamide andbis-(2-methoxyethyl)ether (diglyme). Diglyme is particularly preferred.

Auxiliaries from the series comprising alkali metal halides orcarbonates and alkaline earth metal halides or carbonates are, forexample, potassium carbonate and magnesium carbonate. These auxiliariesare preferably used if sodium phenolate is employed as the startingcompound.

Basic dehydrating agents which can be used in process (2) are, forexample, sodium hydroxide, potassium hydroxide, calcium hydroxide,potassium carbonate, sodium amide, sodium hydride and calcium hydride.

The reaction temperature is kept between 100° and 200° C., preferablybetween about 130° and 170° C., in process (2). The process is usuallycarried out under normal pressure.

About 1 to 1.5 mols, preferably about 1 to 1.2 mol of phenolate, about0.01 to 0.5 mol, preferably about 0.1 to 0.5 mol, of copper catalyst,about 100 to 400 ml of diluent, if appropriate about 0.01 to 0.5 mol ofan auxiliary from the series comprising alkali metal halides orcarbonates and alkaline earth metal halides or carbonates and, ifappropriate, up to about 0.2 mol of a dehydrating agent are usuallyemployed per mol of 3-bromo-4-fluoro-benzaldehyde acetal of the formula(II).

In a preferred embodiment of process (2), the phenolate is initiallyintroduced in a diluent, to which, if appropriate, a dehydrating agenthas been added, the copper catalyst and, if appropriate, the auxiliaryfrom the series comprising alkali metal halides or carbonates andalkaline earth metal halides or carbonates are added and the mixture isheated up to the reaction temperature. The 3-bromo-4-fluoro-benzaldehydeacetal is then metered in and the mixture is stirred until the reactionhas ended. For working up, which can be effected by customary methods,the mixture is diluted, for example with toluene, and filtered and thesolvent is distilled off from the filtrate under reduced pressure,whereupon the crude product remains as the residue.

The new compounds of the formula (I) can be used for the preparation of4-fluoro-3-phenoxybenzaldehyde, which is known as an intermediateproduct for pyrethroids (see DE-OS (German Published Specification)2,709,264). If 4-fluoro-3-phenoxy-benzaldehyde propyleneacetal is used,the preparation of 4-fluoro-3-phenoxy-benzaldehyde by splitting acetalcompounds of the formula (I) with acids can be illustrated by thefollowing equation: ##STR11##

The splitting of the acetal for the preparation of4-fluoro-3-phenoxy-benzaldehyde can be carried out by customary methods.In a preferred procedure, the selected compound of the formula (I) isdissolved in aqueous alcohol and the solution is left to stand at roomtemperature with a catalytic amount of a strong acid, for examplehydrochloric acid. After some hours, a water-immiscible solvent, forexample toluene, is added to the reaction mixture, the organic phase isseparated off, washed with water, dried and filtered and the filtrate isdistilled.

Formula (II) provides a definition of the new3-bromo-4-fluoro-benzaldehyde acetals to be used as intermediateproducts. Preferably, in this formula,

the radicals R individually represent C₁ -C₄ -alkyl or togetherrepresent C₂ -C₅ -alkanediyl, especially --CH₂ --CH₂ --.

If propane-1,3-diol is used, the process described under (5) for thepreparation of the new 3-bromo-4-fluoro-benzaldehyde acetals ("process(5)") can be outlined by the following equation: ##STR12##

Alkanols or alkanediols which can be employed as acetalizing agents inprocess (5) are, for example, methanol, ethanol, propanol and butanol,and ethane-1,2-diol (ethylne glycol) and propane-1,3-diol. Ethyleneglycol is the particularly preferred acetalizing component.

Suitable catalysts are, for example, hydrogen chloride, hydrogenbromide, sulphuric acid, p-toluene-sulphonic acid, boron trifluoride,zinc chloride and acid ion exchange resins.

Suitable water-binding agents are, for example, orthoformic acidtriethyl ester, dimethyl sulphite and chlorotrimethylsilane.

If appropriate, process (5) is carried out in the presence of a diluent.Suitable diluents are, in particular, solvents with which water can beremoved from the reaction mixture by azeotropic distillation. Exampleswhich may be mentioned are benzene, toluene and xylene.

The reaction temperature is between 0° and 150° C. in process (5),preferably between about 20° and 120° C. The process is in generalcarried out under normal pressure.

About 1 to 1.5 molar equivalents, preferably about 1 to 1.2 molarequivalents, of alkanol or alkanediol and, if appropriate, about 2 to 3mols, preferably about 2 to 2.5 mols, of a water-binding agent areemployed per mol of 3-bromo-4-fluoro-benzaldehyde.

In a preferred embodiment of process (5), 3-bromo-4-fluoro-benzaldehyde,the alkanol or alkanediol and a water-binding agent are mixed and themixture is heated for some hours. For working up, which can be effectedby customary methods, the mixture is diluted, for example, with awater-immiscible solvent, for example toluene, the solution is washedwith ice-water, dried and filtered and the filtrate is distilled.

The process for the preparation of 3-bromo-4-fluoro-benzaldehyde from3-bromo-4-fluoro-benzyl alcohol ("process (7)") is preferably carriedout using a diluent. Possible diluents are, if appropriate, water and/oraliphatic or aromatic, optionally halogenated hydrocarbons, for examplepentane, hexane, heptane, cyclohexane, petroleum ether, benzine,ligroin, benzene, toluene, xylene, methylene chloride, ethylenechloride, chloroform, carbon tetrachloride, chlorobenzene ando-dichlorobenzene.

The reaction temperature is between about 0° and 100° C. preferablybetween about 10° and 60° C., in process (7). The process is usuallycarried out under normal pressure.

In a preferred variant (a) of process (7), chromium-(VI)oxide/pyridine/hydrogen chloride (1/1/1) is used as the oxidizing agent.To a solution of this oxidizing agent, for example in methylenechloride, is added a solution of 3-bromo-4-fluoro-benzyl alcohol, alsoin methylene chloride, and the mixture is stirred until the reaction hasended. For working up, the mixture is distilled, if appropriate afterdecanting off undissolved components.

In a second preferred variant (b) of process (7), nitric acid is used asthe oxidizing agent and water is used as the diluent.3-Bromo-4-fluoro-benzyl alcohol is added to this and the mixture isstirred at room temperature for some hours. For working up, the mixtureis rendered alkaline with sodium hydroxide solution and extracted with awater-immiscible solvent, for example toluene, the extract is washedwith water, dried and filtered and the filtrate is distilled.

In a third preferred variant (c) of process (7), chromic acid or amixture of dichromate and sulphuric acid is used as the oxidizing agent.In this case, the diluent is preferably a two-phase system of water andone of the abovementioned organic solvents. Compounds which are suitablefor the transfer of anions from water into organic solvents arepreferably used as catalysts. Examples of these compounds arebenzyl-triethyl-ammonium bisulphate, tetrabutyl-ammonium bromide andmethyl-tricapryl-ammonium chloride (Aliquat 336).

For carrying out process variant (7) (c), 3-bromo-4-fluoro-benzylalcohol is initially introduced in an organic solvent, for examplemethylene chloride, and sulphuric acid, water, catalyst and dichromateare added. The reaction mixture is stirred for some hours. For workingup, the mixture is diluted with water, the organic phase is separatedoff, washed with water, dried and filtered and the filtrate isdistilled.

3-Bromo-4-fluoro-benzyl alcohol and a process for its preparation arethe subject of German Patent Application P 2933985.3 filed Aug. 22, 1979Le A 19 875. This compound is obtained when 3-bromo-4-fluoro-benzoylfluoride is reacted with a complex hydride, for example sodiumtetrahydridoborate, if appropriate using a diluent, for exampleisopropanol, at temperatures between 0° and 50° C. The reaction mixtureis stirred until the reaction has ended, and is diluted with ice-waterand acidified. It is then extracted with a water-immiscible solvent, forexample with methylene chloride, the extract is dried and filtered andthe filtrate is distilled.

The 3-bromo-4-fluoro-benzoyl fluoride to be used as the startingcompound is the subject of German Patent Application P 2,915,738 Le A 19590. This compound is obtained when 4-chloro-benzoyl chloride isconverted into 4-fluoro-benzoyl fluoride by reaction with potassiumfluoride and the 4-fluoro-benzoyl fluoride is brominated to give3-bromo-4-fluoro-benzoyl fluoride, according to the equation below:##STR13##

4-Chloro-benzoyl chloride is reacted with potassium fluoride, forexample in tetramethylene sulphone, at temperatures between 200° and220° C. and the reaction mixture is worked up by distillation.4-Fluoro-benzoyl fluoride of boiling point 53° C./20 mbars (refractiveindex: n_(D) ²⁰ =1.4792) is obtained.

4-Fluoro-benzoyl fluoride is reacted with elementary bromine in thepresence of 1% of iron(III) chloride at 70° to 75° C. In the case of abatch of 1 mole, after distillation, 40 g of unchanged starting materialare recovered and 182 g of a mixture of 3-bromo-4-fluorobenzoyl fluoride(boiling point: 82°-83° C./15 mbars; refractive index: n_(D) ²⁰ =1.5315;melting point: 32°-34° C.) and 3-bromo-4-fluoro-benzoyl bromide (boilingpoint: 123° C./15 mbars; melting point: 35°-37° C.) are obtained.

In principle, the 3-bromo-4-fluoro-benzaldehyde(III) to be preparedaccording to process (7) can also be obtained by other methods, forexample by bromination of 4-fluoro-benzaldehyde or by side chainhalogenation of 3-bromo-4-fluoro-toluene, followed by a Sommeletreaction.

Preparative Examples EXAMPLE 1 ##STR14## Variant (a)

A solution of 45.9 g (0.225 mol) of 3-bromo-4-fluoro-benzyl alcohol in45 ml of methylene chloride was added dropwise to a suspension of 78 gof pyridine/CrO₃ /HCl in 450 ml of methylene chloride. During thisaddition, the temperature of the mixture rose to about 40° C. Themixture was then subsequently stirred for 1 hour, the organic phase wasdecanted from the chromium salts and the solvent was distilled off invacuo. The residue was distilled. 39 g (86% of theory) of3-bromo-4-fluoro-benzaldehyde with a boiling point of 63°-65° C./0.3 mmHg were thus obtained.

Variant (b)

10.2 g (0.05 mol) of 3-bromo-4-fluoro-benzyl alcohol were added to amixture of 10 g of nitric acid (density: 1.4) and 5 ml of water at30°-35° C. and the mixture was then stirred at room temperature for 5hours. After adding 30 g of ice, sodium hydroxide solution was added tothe mixture until the pH value reached 13, and the mixture was thenextracted by shaking with 200 ml of toluene. The organic phase waswashed three times with 50 ml of water each time, dried over sodiumsulphate and then evaporated. The residue was distilled. 6.1 g (60% oftheory) of 3-bromo-4-fluoro-benzaldehyde were thus obtained in the formof an oil which slowly solidified and had a melting point of 29°-31° C.

Variant (c)

A mixture of 29.4 g (0.3 mol) of sulphuric acid, 50 ml of water and 2 mlof Aliquat 336 (tricapryl-methyl-ammonium chloride) was added to asolution of 20.5 g (0.1 mol) of 3-bromo-4-fluoro-benzyl alcohol in 250ml of methylene chloride at room temperature. Thereafter, 9.7 g (0.033mol) of potassium dichromate were added to the reaction mixture and thetemperature was kept at about 25° C. for 2 hours by cooling slightly.After adding 100 ml of water, the organic phase was separated off andthe aqueous phase was extracted once more with 100 ml of methylenechloride. The organic phases were washed twice with 100 ml of water eachtime, then once with 100 ml of saturated sodium bicarbonate solution andonce more with 100 ml of water, dried over sodium sulphate andevaporated in vacuo. The residue was distilled. 16.3 g (81% of theory)of 3-bromo-4-fluoro-benzaldehyde were obtained in this manner as acolorless oil with a boiling point of 65° C./0.3 mm Hg.

EXAMPLE 2 ##STR15##

62 g of 4-fluoro-benzaldehyde were added dropwise to a mixture of 166 gof aluminum chloride and 150 ml of 1,2-dichloroethane at an internaltemperature of 30° C. and the mixture was subsequently stirred for about30 minutes. 88 g of bromine were then added dropwise at an internaltemperature between 30° and 40° C. The reaction mixture was subsequentlystirred for about 2 hours and then poured onto ice. After separating offthe organic phase, the aqueous phase was then extracted with1,2-dichloroethane. The combined organic phases were washed with water,dried with sodium sulphate and filtered. After distilling off thesolvent from the filtrate under reduced pressure, a crude product which,according to analysis by gas chromatography, contained 78.8% of3-bromo-4-fluoro-benzaldehyde and 17.6% of 4-fluoro-benzaldehyde wasobtained as the residue. After vacuum distillation, 58 g of3-bromo-4-fluoro-benzaldehyde of boiling point 108° C./25 mbars and ofrefractive index n_(D) ²⁰ : 1.5737 were obtained. The product graduallysolidified: melting point: 30°-31° C.

EXAMPLE 3 ##STR16##

26 g (0.24 mol) of trimethylchlorosilane were added to a mixture of 20.3g (0.1 mol) of 3-bromo-4-fluoro-benzaldehyde and 6.8 g (0.11 mol) ofethane-1,2-diol and the mixture was heated to 100° C. for 3 hours. Aftercooling to room temperature, 100 ml of toluene were added and themixture was shaken twice with 50 ml of ice-water each time. The organicphase was dried over sodium sulphate and evaporated in vacuo. Theresidue was distilled in vacuo. 21 g (85% of theory) of3-bromo-4-fluoro-benzaldehyde ethyleneacetal were thus obtained in theform of a colorless oil with a boiling point of 79°-81° C./0.1 mm Hg.

EXAMPLE 4 ##STR17##

To dehydrate a suspension of 3.2 g (27.5 mmol) of sodium phenolate in 3ml of diglyme, 0.1 g (3.5 mmol) of sodium hydride was added, and 0.05 gof copper(I) oxide (0.35 mmol) and 0.5 g (6.5 mmol) of potassiumchloride were then added to the mixture. The reaction mixture was heatedto 155° C. under an inert gas (for example argon), and 6.2 g (25 mmol)of 3-bromo-4-fluoro-benzaldehyde ethyleneacetal were added at thistemperature. The mixture was subsequently stirred at 155° C. for 7 hoursand, after cooling to room temperature, 50 ml of toluene were added andthe inorganic material was filtered off. The filtrate was freed fromsolvent in vacuo. 6.0 g of a product containing 87% of4-fluoro-3-phenoxy-benzaldehyde ethyleneacetal were thus obtained(corresponding to a yield of 80% of theory).

EXAMPLE 5 ##STR18##

A solution of 26 g (0.1 mol) of 4-fluoro-3-phenoxy-benzaldehydeethyleneacetal in 60 ml of ethanol, 20 ml of water and 1 ml ofconcentrated hydrochloric acid was stored at room temperature for 3hours. The ethanol was then distilled off in vacuo, and 100 ml oftoluene were added to the residue. The water was separated off and theorganic phase was washed twice with 50 ml of water each time, dried oversodium sulphate and evaporated in vacuo. The residue was distilled invacuo. 19.6 g (91% of theory) of 4-fluoro-3-phenoxy-benzaldehyde wereobtained in this manner in the form of a colorless oil with a boilingpoint of 102°-104° C./0.1 mm Hg.

It will be appreciated that the instant specification and examples areset forth by way of illustration and not limitation, and that variousmodifications and changes may be made without departing from the spiritand scope of the present invention.

What is claimed is:
 1. 3-Bromo-4-fluoro-benzaldehyde of the formula##STR19##